The invention concerns a magnetic drive with at least one armature magnetized in the direction of excursion and consisting of a permanent magnet with two magnetically soft pole pieces, said armature being movable along a common axis between two electromagnetic external pole-pieces which are magnetizable always with the same polarity and are axially located inside a passage of a third electromagnet that is present between the external pole-pieces and that can be controlled with a magnetic polarity that is opposite that of the said external pole-pieces, the central annular pole-piece comprising passages and/or the external pole-pieces projecting from a coil wound on a magnetically soft core.
Such a magnetic drive is known from the British patent 1,068,610.
The state of the art contains moreover numerous magnetic drives with armatures made of permanent magnetic materials and displaceable between two pole-pieces of the same sign. Essentially the basic designs of simple magnetic circuits of this sort have been exhausted. However there are almost no reliable practical computation methods or design criteria, and this kind of magnetic drive so far has found little acceptance, in considerable part because of mechanical inadequacies, the use of earlier magnetic materials of lower performance.
The German Offenlegungsschrift 34 26 688 discloses a magnetic drive of the above species with two cylindrical, coaxial and sequentially mounted coils and a permanent-magnet armature which is displaceable centrally in the axial direction inside the coil bore. This arrangement of two coils hardly allows mounting operational devices at the magnetic armature for lack of adequate space inside the coil bore. Moreover there is danger of the magnetic armature heating on account of the unfavorable position and thereby losing its permanent field strength.